7.0 References for the Mk7 GTI Intercooler Test
A. Test FAQ
Addressing questions raised during testing of the intercoolers.
Q. How do you get useful information with the bench temperature test if it doesn’t recreate the conditions on the car?
A. Testing covers a wide range of methods that can be categorized as developmental test and operational test. Developmental testing focuses on meeting technical requirements within a controlled setting to minimize the chances of unmeasured variables affecting system performance. It is performed to demonstrate various aspects of specified system performance. The developmental test is structured to hold many things constant, isolate others, and allow measurement of one or two parameters of interest. The bench test is a developmental type of test.
Operational test focuses on verifying specific operational requirements under realistic conditions. The system is tested while performing typical operating tasks in a realistic environment. The system under test is generally put into a larger system of systems which may limit time or resources for collecting the data needed to perform root cause analysis. Installing an intercooler on the GTI and driving on the street is an example of operational testing.
Developmental testing decreases technical risks and improves the likelihood of conducting a successful operational test.
With limited resources to apply to testing and a goal of finding the best intercooler for the GTI among numerous options, developmental testing on the bench helps identify candidate products that are more likely to meet operational performance goals.
B. Intercooler Supplier Statements
Wagner – “This Intercooler Kit is the best choice when it comes to performance gains and low intake temperatures and also the right thing for racing.”
Racingline – “Our massive ‘plate & bar’ Intercooler System is the best performing intercooler upgrade on offer for the MQB-platform Golf 7 GTI, R and Audi S3.”
Integrated Engineering – “As a result, the IE FDS intercooler has been proven to reduce intake air temperatures more so than other units available, thus offering the largest power gains possible.”
AMS – “The AMS Golf R intercooler is the ultimate choice to keep your “Hot Hatch” cool!”
C. Bell Intercooler FAQ Excerpts
C-1: Efficiency (of an intercooler)
How much heat is removed.
The closer the post-intercooler intake air temperature gets to the ambient air temperature the more thermally efficient the intercooler.
These outlet temps will continue to rise slowly over the duration of the increased intake air temperature event until the thermal inertia of the intercooler is overcome, at which point the outlet temps will rise sharply to a stabilized temperature. This new stabilized temperature reflects the thermal efficiency of the intercooler.
Thermal inertia is the amount of time required between an increase in the intercooler inlet temperature (from increased boost pressure and/or engine rpm) and the subsequent increase in intercooler outlet temperature.
If the increased intake air temperature is removed prior to overcoming the thermal inertia of the intercooler the outlet temperatures will never reach the thermal efficiency temperature.
C-2: Pressure Drop
Is the measure of the internal resistance of the intercooler or how much energy or boost pressure is lost as the intake air passes through the intercooler system.
Resistance at the intercooler core is directly related to two elements: internal flow area and internal resistance. Internal flow area is the amount of space available for the air to move through the core. The larger the internal flow area, the lower the resistance and the lower the pressure drop. The smaller the area, the higher the resistance and higher the pressure drop. Internal resistance, as you might reason, is the resistance encountered within the intercooler core. This is primarily the result of the internal cooling fin design and density with a secondary source being potential restrictions at the entry point to the core.
C-3: Efficiency versus Pressure Drop
Regardless of the efficiency, if too much pressure is lost, then the intercooler is either useless or can actually decrease performance.
The merit of a core is it’s efficiency versus its internal drag characteristics.
The most heat comes out of the tube where the temperature difference between the inside and the outside is the greatest. That exists in the first couple inches of the tube. The last inch of the tube, wherein the charge temperature is rapidly approaching the cooling media temperature, will transfer very little heat, thus being of minor use.
C-4: Frontal area:
This is a rapidly decreasing function. If the proper core size is used, then doubling it will definitely not double the efficiency. More likely, doubling the core would raise the efficiency about 5% and cost twice the necessary amount and add substantially to the weight.
C-5: Plate area:
Plate Area (the sum of the Core-Plate Area which is exposed to the Atmosphere) is directly proportional to the frontal area and the thickness. Thickness, however, is a double-edged sword. With the greater thickness, the plate area increases but less ambient air can penetrate the thicker core to offer cooling.
C-6: Ambient air quantity
It is very important to insure that air coming in the snout of the car will actually go through the intercooler.
A proper duct is probably the single most beneficial thing that can be done to an existing intercooler. Positioning in the main stream of ambient air is crucial. By comparison, a taped up intercooler with no ambient air flow will offer only about 20% efficiency.
A typical air-to-air intercooler for a street application achieves between 60% and 70% efficiency, an excellent/optimum design for road racing can approach close to 90% efficiency, but requires an adequate “budget!”
The efficiency is defined as the ratio of the temperature removed from the air charge by the intercooler relative to how much temperature is put into the charge by the turbo/supercharger.
For example: If the turbo/supercharger puts 150 degrees F into the charge when compressing the air, and the intercooler removes 110 of those degrees, then the efficiency is: Eff = 110 / 150 = .733, or 73.3%
When configuring the orientation of the core in a given space, always position the core to offer the shortest length tube and the most number of tubes.